More then 17% of pregnant women in the USA smoke and/or use nicotine replacement therapies. Although tobacco contains many harmful substances, nicotine not only underlies the addictiveness of tobacco consumption, it also has neurotoxic and neuroteratogenic effects on the developing brain. In animal models, exposure to nicotine during early development provokes behavioral deficits in offspring that resemble those reported in children after maternal nicotine consumption. Such behavioral impairments, most notably hyperlocomotor activity, are compellingly consistent with malfunctioning of the midbrain dopamine system and its cholinergic innervation, for which nicotine is an agonist. However, no studies to date have examined whether developmental nicotine induces structural alterations in these two cell groups that persist into adulthood. The central hypothesis guiding this proposal is that long-term behavioral impairments following nicotine exposure at particular developmental stages result from underlying morphological alterations of the brainstem dopamine and cholinergic systems. To test this hypothesis using light and electron microscopy, we will conduct the first unbiased stereological assessments of brainstem neurons in adult rats treated with nicotine prenatally or in the early postnatal period, which correspond approximately to the first and second halves of human pregnancy. We will also examine the cholinergic axons communicating between the mesopontine tegmentum (MP) and dopamine cells in the ventral tegmental area (VTA) as well as total excitatory and inhibitory synapses. In Aim 1, we will determine the persitent structural consequences of nicotine exposure during E4-E21 on the VTA and/or MP of adult animals. Aim 2 will examine the persistent structural consequences of nicoitne exposure during P1-P14 on the VTA and/or MP of adult animals. For both aims, we will measure a comprehensive set of cellular and phenotypic parameters in both the VTA and MP and will correlate anatomical measurements with behavioral assessments of locomotor activity in individual animals. The outcome of the proposed studies will allow specific predictions regarding changes in the human brain following prenatal nicotine exposure and facilitate the development of medical treatment strategies for the offspring of smokers by demonstrating the morphological impact on the brain regions that are most likely to be primarily and persistently affected. Pregnant women who smoke or who use nicotine replacement therapy during pregnancy expose their infants to neuroteratogenic effects of nicotine that can result in learning disabilities and behavioral abnormalities. This proposal uses an animal model of early nicotine exposure to examine structural damage in the brain regions that regulate cognitive function, motivated behaviors, and liability for later addiction. The data obtained in these studies will facilitate the development of medical treatment strategies for the children of smokers by revealing the brain regions that are most fundamentally affected by early nicotine exposure. [unreadable] [unreadable] [unreadable]